1. Field of the Invention
The present invention relates to a forwarding apparatus and a forwarding method.
2. Description of the Related Art
A commonly used forwarding apparatus such as a router, a gateway, an ether switch etc., which forwards data between the forwarding apparatus itself and another forwarding apparatus via a network, uses destination data included in a received frame to search a transfer condition and forwards the frame according to the transfer condition (for example, see Japanese Patent Application Laid-open No. 2006-108985).
A specific example is explained with reference to FIG. 12. FIG. 12 is a schematic for explaining a forwarding apparatus according to a conventional technology. As shown in FIG. 12, a forwarding database (FDB), which is a storage device for searching for the transfer condition using the destination data, stores therein a frame table and a transfer condition table. To be specific, the frame table stores therein a plurality of entries by establishing a correspondence between frame identification data and an address. The frame identification data includes a virtual local area network identifier (VLAN ID) (for example, 100) that is data of a destination network, and a media access control identifier (MAC ID) (for example, A) that is data of a destination terminal. The address (for example, addr#01) is an identifier for searching for the transfer condition. The transfer condition table establishes and stores therein a correspondence between the transfer condition and the address. The transfer condition includes a destination port (for example, port#01) that is data of an output port that forwards the frame to the destination network and a process content (for example, transfer) of input data.
Upon receiving the frame, a hardware unit in the forwarding apparatus according to the conventional technology reads the VLAN ID (for example, “VLAN ID”=“103”) and the MAC ID (for example, “MAC”=“D”) (see (1) of FIG. 12). Next, the forwarding apparatus searches for the address among all the entries from the frame table. In the example that is explained with reference to FIG. 12, the forwarding apparatus checks all the entries under the condition “VLAN ID”=“103” and “MAC ID”=“D” (see (2) of FIG. 12) and searches for “addr#04” that is the address of the appropriate entry (see (3) of FIG. 12). Next, the forwarding apparatus uses the transfer condition table and the searched address to search for the transfer condition (for example, “port#01” and “transfer”). In the example explained with reference to FIG. 12, the forwarding apparatus checks the transfer condition table under the condition “addr#04” (see (4) of FIG. 12) and searches for the transfer condition “port#04” and “transfer” (see (5) of FIG. 12). Further, based on the searched transfer condition, the forwarding apparatus executes a transfer process on the frame (in the example shown in FIG. 12, the forwarding apparatus transfers the frame from the port#04 (see (6) of FIG. 12)).
If a structure of the network is modified, a portion of the FDB is deleted due to an operation from the forwarding apparatus according to the conventional technology or an external device, or the FDB is overwritten, thus getting updated. To be specific, if a single area on the network is annihilated, the FDB gets updated by sequentially deleting each entry related to the annihilated area using the operation from the forwarding apparatus according to the conventional technology or the external device.
However, in the conventional technology mentioned earlier, a throughput of the entire forwarding apparatus is adversely affected due to the updation of the FDB.
In other words, because the frame table in the FDB includes a combination of the VLAN ID, the MAC ID, and the address, the frame table stores therein a large amount of data, thus necessitating a content addressable memory (CAM) that is a device that exclusively stores therein the FDB. Because the forwarding apparatus according to the conventional technology updates the FDB for each single entry, the FDB needs to be repeatedly updated for the number of entries that are stored by the FDB. Thus, in the forwarding apparatus according to the conventional technology, a time period passes until the complete updation of the FDB, thereby resulting in occurrence of a time lag. Due to this, a mismatch occurs between a timing to search for the address and a timing to search for the transfer condition. Especially, when mirroring the FDB using a plurality of physically different CAM, because the FDB in the multiple CAM need to be updated at the same time, updation of the FDB requires a long time period and results in a significant mismatch at the time of searching for the transfer condition. Thus, in the forwarding apparatus according to the conventional technology, the throughput of the entire forwarding apparatus is adversely affected due to occurrence of the mismatch at the time of searching for the transfer condition.